Determining a user's position inside of a building can be very challenging if the building is large and the user is new to the surroundings. Various approaches have been attempted to determine a user's position in a building. For example, inertial guidance systems have been used. Typical inertial guidance systems use a combination of accelerometers and gyroscopes to measure acceleration and rotation. These measurements are then integrated to obtain measurements of position. However, all inertial guidance systems suffer from integration drift which magnifies small errors in acceleration and rotation measurements that increases unbounded over time. Any error becomes larger as successive measurements are integrated.
Another approach has been to use dead-reckoning. Dead-reckoning methods measure a distance and direction traveled. Then by knowing an initial starting point, the current position can be calculated. However, typical dead-reckoning systems use some type of compass to determine direction. When inside a building, the metal in the building can cause errors in compass measurements of direction. Additionally, since dead-reckoning depends on measuring a path from an initial starting point, dead-reckoning also suffers from integration drift where errors in initial measurements are magnified in subsequent measurements. Other approaches have also been attempted, but suffer from similar and different limitations in accuracy.
Yet another approach has been to use radio frequency (RF) ranging. RF ranging measures either the range of a receiver to multiple transmitters or the range of a single transmitter to several receivers. After measuring the range, a triangulation computation is performed. RF ranging does not suffer from integration drift and grow over time, but RF ranging suffers from incorrect range measurements due to multi-path issues and difficulties in receiving the signal.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an efficient and effective navigation system that can be used inside a building.